Prius III - fog lights and warranty

I can not speak for Toyota, but I couldn't see how adding Fog Lights could invalidate the warranty of things like the transmission...now if you cut into the wiring harness and did something to short the electrical system it is on you.

If you tapped a new line (fused of course) off the 12v battery or 12 volt outlet, and ran it to your own switch you really did not modify any of Toyota's equipment, just the blank on the bumper, which if any body issues came about at the blank they could squirm out of the warranty repair, but I don't see how they could make a case for a computer system failure any more than they could say your plugging in a cellphone charger caused a computer failure.
This would be the case so long as you did not damage any of the Toyota wiring or equipment, for instance if you drilled through the fire wall into an electrical module or board or wiring harness.

You could save the original blanks, and remove your fog lights in the event of a major warranty issue,and put it back like new before taking it in for warranty work, also.

Keep in mind, I am not a lawyer, this is just my opinion. You could ask your dealer, if you did the work in such a way not to tamper with original equipment, would they honor warranty as long as you did not directly cause any warranty damage or defect.

Team Toyota in Langhorne PA will cut a hole in your Prius Roof and put in a Sun Roof on a brand new Prius if you want and will not effect the warranty, I don't see how they could make a case for Fog Lights voiding the warranty. IMHO.